Domestic electric heating appliance



Dec. 24, 1963 J. w. JACOBS DOMESTIC ELECTRIC HEATING APPLIANCE Filed Nov. 25. 1960 INVENTOR. James [11 Jamie BY we rrqw" United States Patent 3,115,566 DUMESTTC ELECTRHC HEATENG APPLIANCE James W. Jacobs, Dayton, Ohio, assignor to General Motors Corporation, Detroit, Mich, a corporation of Delaware Filed Nov. 25, 196i), Ser. No. 71,582 5 Claims. (Cl. 2192ll) This invention relates to a domestic appliance and more particuarly to an improved infinite heat control for a surface cooking unit.

Many electric ranges in use today utilize an infinite heat switch for controlling the surface cooking units. Such a switch is effective to provide a full range of power inputs to the cooking unit so that the exact heat output required is available by simply manipulating a control knob. In general, infinite heat switches are of the pulsing type wherein a bimetal actuated cycler contact is in power supply relationship with the surface cooking unit. In accordance with the percentage of open to closed time for the switch, the surface cooking unit will put out more or less heat. One of the more common infinite heat switches has a pair of contacts, one of which is carried on a bimetal element fixed at one end thereof. The cycler contacts carry the full power supply to the surface cooking unit. A users knob permits selection of the desired average watts input to the surface unit and the knob is effective as follows. Two internal cams are moved by the users knob and they individually close the contacts to the surface unit when the knob is turned to any On position. In addition, they apply the necessary mechanical pressure to the bimetal cycler contacts, thus regulating the length of time per cycle that the surface units is energized. In this prior art device, a heater is provided for the bimetal and is energized so long as the bimetal actuated cycler contacts to the surface cooking unit are closed. After a time interval, depending upon the users knob setting, the bimetal cycler is suificiently heated by its heater to cause the bimetal to Warp and open the circuit through the surface unit. As the bimetal cools, it returns to its normal shape, thus reclosing the contacts completing the circuit through the surface unit. Only in the high setting is the bimetal switch locked closed so that the unit operates continuously. It has been found that this prior art arrangement too easily loses its calibration and lacks the sensitivity which is desirable in cooking operations.

Accordingly, it is an object of this invention to provide an infinite heat control for an electric cooking unit which has an increased sensitivity to closely regulate cooking temperatures.

It is a general object of this invention to provide an infinite heat cooking unit control with a variable timing circuit.

It is a more specific object of this invention to provide an infinite heat cooking unit control with a transistor diode timing circuit including a four-layer, hyperconductive negative resistance transistor diode for controlling the pulsing rate at which power is supplied to the surface cooking unit.

Further objects and advantages of the present invention will be apparent from the following description, reference being had to the accompanying drawings wherein a preferred embodiment of the present invention is clearly shown.

in the drawings:

FIGURE 1 is a fragmentary elevational view of a tubular sheathed heating element suitable for use with this invention.

FIGURE 2 is a schematic wiring diagram of the control of this invention.

In accordance with this invention and with reference to FIGURE 1, an electric range is illustrated as hav- Hal ing a conventional tubular sheathed heating element, such as 12, supported in an opening 14 in the top of the range. The surface cooking unit or heating element 12 is adapted to be controlled by an infinite heat switch in which infinitely variable amounts of power are pulsed or intermittently supplied to the heating unit 12 in accordance with a predetermined setting. A conventional domestic power supply of 230 volts is used to energize the surface cooking unit 12 and it is to the control of this power supply in accordance with a preselected cooking heat setting that this invention is directed.

Referring now to FIGURE 2, the infinite heat control of this invention will be clearly described. A 230 volt domestic power supply is illustrated in FIGURE 2 as L L and N. interposed between the power supply and the surface cooking unit 12 is an infinite heat switch, designated generally as in. The control 16 may be positioned on the console or control panel of an electric range so that a control knob 18 will be accessible for the operator. The knob ll? is in operative engagement with a first cam surface 2d and a second cam surface or protuberance 22, the latter of which is operative to shut off and deenergize the cooking unit 12 while the former provides the infinite bias to the bimetal to condition the switch for infinite heat control.

The infinite heat switch 16 is comprised further of a bimetal or thermally responsive device 24 which is afiixed as at one end The bimetal member carries a first control contact 2.8 and a first power supply contact 3d. The contact 28 opens and closes on a fixed second control contact 32 while the first power supply contact 30 opens and closes a fixed second power supply contact 34. Thus, it may be seen that power supply on the 230 volt circuit L L leading to the surface cooking unit 112 is interrupted at the pulsing power supply contacts 30, 34. In heat transfer relationship to the bimetal 24 is a bimetal heater 3d, the heat output of which actuates the bimetal element. It should be noted that the bimetal 24 is in its normal or cold position in FIGURE 2. As heat is applied to the bimetal 24 from the heater 3'6, the bimetal will warp in a manner to move the contacts 255 and 3t away from the contacts 32 and 34, respectively.

The control circuit which is effective to determine the heat output of the bimetal heater 36 includes a fourlayer, hyperconductive negative resistance transistor diode in series with the bimetal heater 36. In parallel with the diode 33 is a capacitor ll]. The heating element as, the diode 38 and the capacitor 4d form a variable parallel timing circuit, designated generally as 42. The timing circuit 4-2 is effective to pulsingly control the current to the heater 36, thereby regulating the amount of heat output of the heater and thus the opening and closing or pulsing rate of the bimetal actuated cycler contacts 28 and 36).

in order to regulate the pulsing rate of the timing circuit 4-2 in accordance with the heat output setting at the knob 18, a rheostat or variable resistance 44- is included in series with the parallel timing circuit 42. The rheostat 44 includes a wiper blade as which is manipulated through a linkage id and the bias of cam surface 20 as the control knob 18 is rotated. As the knob is rotated, the greater the resistance 44 placed in series with the timing circuit 42, the slower will be the capacitive pulsing rate of current to the heater 36. Thus, the bimetal 24 will maintain the contacts 3%, 34 closed for longer periods to provide a longer percentage of On time for the surface cooking unit 12. Conversely, the smaller the resistance preset on the rheostat 44-, the faster will be the current pulsing rate to the heater and the surface unit 12 will be energized for lesser outputs.

The capacitive timing circuit 42 is operated by an alternating domestic power supply L L and N, and thus requires a rectifier 5d properly oriented with the diode 33 to provide direct cturent pulses for charging the capacitor 49, Although, the foregoing description of the capacitive timing circuit 42 is believed sufiicient for the purposes of this disclosure, additional details relating to the operating theory of a capacitive timing circuit are set forth in a concurrently filed application SN. 71,581, filed November 25, 1960, and assigned to the same assignee as this invention.

When it is desired to turn the surface cooking unit 12 off, the operators knob 18 is turned so that the protuberance 22 will bias the bimetal 24 through the linkage 54 to a positively open position. At all other times, the pulsing rate of the power supply contacts 30, 34 and the timing circuit control contacts 28, 32 is governed by the heat output of the heater as rather than by a mechanical bias of the bimetal as has been used in the prior art.

In operation, a user will rotate the knob I13 to the desired heat output setting, namely, Low, Medium-Low, Medium, Medium-High or High. In accordance with the selected setting, the rheostat wiper 46 is positioned along the rheostat resistance 44. Since the surface cooking unit 12 is cold, 230 volt power will flow from L surface cooking unit 12, power supply contact 34, power supply contact 30, the bimetal 24 and conductor 56 to the other side of the line L The surface cooking unit will immediately start to heat. At the same time, the control circuit is energized through the control contacts 28 and 32. Half-sine wave 115 volt power increments are passed by the rectifier 50 from the neutral N to the rheostat wiper 46 and, thus, the rheostat resistance 4d. This setting regulates the increments of power which are passed to and stored by the capacitor 6. When the stored potential within the capacitor reaches the firing voltage of the diode 38, the discharging current will avalanche through the heated 36the circuit being completed through the control circuit conductor 60, the control contacts 28 and 32,, the bimetal 24 and conductor 56 to the other side of the line L In accordance with the firing rate through the diode 38, the heat output of the heater is regulated, and this heat output causes the flexing or warping of the bimetal 24 which selectively opens and closes the power supply circuit to the surface cooking unit 12.

It should now be seen that an infinite heat switch with improved sensivity has been provided wherein a capacitive timing circuit is utilized to pulse increments of power to a heater for thermally responsively actuating a bimetal cycler in a power supply circuit.

While the embodiment of the present invention as herein disclosed, constitutes a preferred form, it is to be understood that other forms might be adopted.

What is claimed is as follows:

1. In combination with an electric cooking unit adapted to support a utensil, a thermally responsive control comprising, a first and second contact forming a first pulsing switch, a second and third contact forming a second pulsing switch connected to said cooking unit, bimetal means for opening and closing said pulsing switches, a heater for actuating said bimetal means, a negative resistance diode connected in series with said heater, said diode having a predetermined switching voltage, a capacitor connected in a parallel circuit with the heater and diode, said capacitor being capable of being charged to a voltage great enough to exceed the switching voltage of said diode, a rheostat for controlling the charging rate of said capacitor to regulate said cooking unit, a rectifier connected in series with said rheostat, said parallel circuit and said bimetal means and oriented to prevent flow of current through said diode before said diode reaches its switching voltage, and an alternating current power supply having a peak output voltage greater than the switching voltage of said diode and including a first line conductor and a neutral line conductor for supplying energy to said bimetal means and said rectifier for repeatedly A; energizing said heater and a second line conductor in series with said cooking unit and said second pulsing switch for supplying energy selectively to said cooking unit, said negative resistance diode being in the form of a fourlayer transistor.

2. In combination with an electric cooking unit adapted to support a utensil, a thermally responsive control comprising, a first and second contact forming a first pulsing switch, a second and third contact forming a second pulsing switch connected to said cooking unit, bimetal means for opening and closing said pulsing switches, a heater for actuating said bimetal means, a negative resistance diode connected in series with said heater, said diode having a predetermined switching voltage, a capacitor connected in a parallel circuit with the heater and diode, said capacitor being capable of being charged to a voltage great enough to exceed the switching voltage of said diode, a rheostat for controlling the charging rate of said capacitor to regulate said cooking unit, a rectifier connected in series with said rheostat, said parallel circuit and said bimetal means and oriented to prevent fiow of current through said diode before said diode reaches its switching voltage, and an alternating current power supply having a peak output voltage greater than the switching voltage of said diode and including a first line conductor and a neutral line conductor for supplying energy to said bimetal means and said rectifier for repeatedly energizing said heater and a second line conductor in series with said cooking unit and said second pulsing switch for supplying energy selectively to said cooking unit.

3. In combination with an electric cooking unit adapted to support a utensil, a cooking unit control comprising, a first and second contact forming a first pulsing switch, a second and third contact forming a second pulsing switch connected to said cooking unit, thermally responsive means for opening and closing said pulsing switches, a

heater for actuating said thermally responsive means, a

negative resistance diode connected in series with said heater, said diode having a predetermined switching voltage, a capacitor connected in a parallel circuit with the heater and diode, said capacitor being capable of being charged to a voltage great enough to exceed the switching voltage of said diode, a rheostat for controlling the charging rate of said capacitor to regulate said cooking unit, a rectifier connected in series with said rheostat, said parallel circuit and said thermally responsive means and oriented to prevent flow of current through said diode before said diode reaches its switching voltage, and an alternating current power supply having a peak output voltage greater than the switching voltage of said diode and including a first line conductor and a neutral line conductor for supplying energy to said thermally responsive means and said rectifier for repeatedly energizing said heater and a second line conductor in series with said cooking unit and said second pulsing switch for supplying energy selectively to said cooking unit.

4. In combination with an electric cooking unit adapted to support a utensil, a cooking unit control comprising, a first and second contact forming a first pulsing switch, a second and third contact forming a second pulsing switch connected to said cooking unit, thermally responsive means for opening and closing said pulsing switches, a heater for actuating said thermally responsive means, a negative resistance diode connected in series with said heater, said diode having a predetermined switching voltage, a capacitor connected in a parallel circuit with the heater and diode, said capacitor being capable of being charged to a voltage great enough to exceed the switching voltage of said diode, a rheost-at for controlling the charging rate of said capacitor to regulate said cooking unit, a rectifier connected in series with said rheostat, said parallel circuit and said thermally responsive means and oriented to prevent flow of current through said diode b fore said diode reaches its switching voltage, and an alternatin g current power supply having a peak output voltage greater than the switching voltage of said diode and including first conductor means for supplying energy to said thermally responsive means and said rectifier for repeatedly energizing said heater and second conductor means in series with said cooking unit and said second pulsing switch for supplying energy selectively to said cooking unit.

5. In combination with an electric cooking unit adapted to support a utensil, a cooking unit control comprising, a first and second contact forming a first pulsing switch, a second and third contact forming a second pulsing switch connected to said cooking unit, thermally responsive means for opening and closing said second pulsing switch, said first pulsing switch opening and closing simultaneously with said second pulsing switch, a heater for actuating said thermally responsive means, a negative resistance diode connected in series with said heater, said diode having a predetermined switching voltage, a capacitor connected in a parallel circuit with the heater and diode, said capacitor being capable of being charged to a voltage great enough to exceed the switching voltage of said diode, a rheostat for controlling the charging rate of said capacitor to regulate said cooking unit, a rectifier connected in series with said rheost at, said parallel circuit and said first pulsing switch and oriented to prevent fio w of current through said diode before said diode reaches its switching voltage, and an alternating current power supply having a peak output voltage geater than the switching voltage of said diode and including first conductor means for supplying energy to said thermally responsive means and said rectifier for repeatedly energizing said heater and second conductor means in series with said cooking unit and said second pulsing switch for supplying energy selectively to said cooking unit.

References Cited in the file of this patent UNITED STATES PATENTS 2,866,106 Schulr Dec. 23, 1958 2,947,916 Beck Aug. 2, 1960 2,970,201 Woodward Iran. 31, 1961 3,018,356 Busch et a1. Jan. 23, 1962 3,030,523 Pittman Apr. 17, 1962 

5. IN COMBINATION WITH AN ELECTRIC COOKING UNIT ADAPTED TO SUPPORT A UTENSIL, A COOKING UNIT CONTROL COMPRISING, A FIRST AND SECOND CONTACT FORMING A FIRST PULSING SWITCH, A SECOND AND THIRD CONTACT FORMING A SECOND PULSING SWITCH CONNECTED TO SAID COOKING UNIT, THERMALLY RESPONSIVE MEANS FOR OPENING AND CLOSING SAID SECOND PULSING SWITCH, SAID FIRST PULSING SWITCH OPENING AND CLOSING SIMULTANEOUSLY WITH SAID SECOND PULSING SWITCH, A HEATER FOR ACTUATING SAID THERMALLY RESPONSIVE MEANS, A NEGATIVE RESISTANCE DIODE CONNECTED IN SERIES WITH SAID HEATER, SAID DIODE HAVING A PREDETERMINED SWITCHING VOLTAGE, A CAPACITOR CONNECTED IN A PARALLEL CIRCUIT WITH THE HEATER AND DIODE, SAID CAPACITOR BEING CAPABLE OF BEING CHARGED TO A VOLTAGE GREAT ENOUGH TO EXCEED THE SWITCHING VOLTAGE OF SAID DIODE A RHEOSTAT FOR CONTROLLING THE CHARGING RATE OF SAID CAPACITOR TO REGULATE SAID COOKING UNIT, A RECTIFIER CONNECTED IN SERIES WITH SAID RHEOSTAT, SAID PARALLEL CIRCUIT AND SAID FIRST PULSING SWITCH AND ORIENTED TO PREVENT FLOW OF CURRENT THROUGH SAID DIODE BEFORE SAID DIODE REACHES ITS SWITCHING VOLTAGE, AND AN ALTERNATING CURRENT POWER SUPPLY HAVING A PEAK OUTPUT VOLTAGE GREATER THAN THE SWITCHING VOLTAGE OF SAID DIODE AND INCLUDING FIRST CONDUCTOR MEANS FOR SUPPLYING ENERGY TO SAID THERMALLY RESPONSIVE MEANS AND SAID RECTIFIER FOR REPEATEDLY ENERGIZING SAID HEATER AND SECOND CONDUCTOR MEANS IN SERIES WITH SAID COOKING UNIT AND SAID SECOND PULSING SWITCH FOR SUPPLYING ENERGY SELECTIVELY TO SAID COOKING UNIT. 